what is wrong with my craftsman charging stand 1421410 for 16.8V battery?

I bought a craftsman cordless drill 16.8V a while back and the charger has gone bad recently. When the battery is plugged in, the LED is lit up for few seconds and turned off. Battery doesn't get charged. I opened up the circuit board, measured on the components and they seemed to be fine (i.e. R2(1/4w)=216ohm, R3(2W)=15ohm, D1(Vfw)=0.55V, NTC=2ohm). Someone in another forum discussion suggested to short out the thermistor for the battery to get charged. Is it true? If so, what is the thermistor there for? I drew out the schematic but couldn't analyze how it works. Another word, how does the charger work? I really appreciate if someone can shed some light on it. Thanks.